Silicon oxide dielectric films form resilient interfaces with silicon and provide high dielectric strength and a relatively low dielectric constant. These traits result in heavy use of silicon oxide for insulating electrically active features from one another. Two conventional methods for depositing a silicon oxide film include: (1) oxidation process wherein silicon is oxidized at relatively high temperatures (e.g., sometimes more than 1000° C.); and (2) a chemical vapor deposition (CVD) process wherein the silicon and oxygen sources are introduced into a chamber and exposed to energy (e.g., heat) to form a silicon oxide film. Silicon oxide CVD processes typically occur at temperatures ranging from 600° C. to 800° C. or below 450° C. depending on the application. While satisfactory for larger integrated circuit linewidths, these methods can cause diffusion at interfaces due to the high deposition temperature, thereby degrading electrical characteristics of miniature electrical devices.
In addition to lower substrate temperatures, thin films used in semiconductor devices will increasingly require atomic layer control during deposition due to the decreasing linewidths. These thin films will also be required to have excellent step coverage and conformality. To satisfy the requirements, atomic layer deposition (ALD) process have gained traction in semiconductor manufacturing.
ALD silicon oxide films have been deposited at a temperature of more than 600K via the atomic layer deposition process using SiCl4 and H2O sources. In this exemplary prior art process, a SiCl4 source is provided in a substrate processing region containing a substrate having hydroxyl groups (—OH) on its surface. The SiCl4 source reacts with the hydroxyl group in this first deposition step, and —SiCl3 is adsorbed on the surface of the substrate, HCl by-products are formed. When the reaction of SiCl4 with the hydroxyl group is essentially complete, a monolayer of Si has been added to the surface of the substrate. Further exposure to SiCl4 results in insignificant additional deposition. Such a reaction is referred to as self-limiting. At this point, the surface of the substrate is terminated with —SiCl3 surface chemical species.
An H2O source is then flowed into the substrate processing region. H2O reacts with the —SiCl3 surface chemical species to generate adsorption of the hydroxyl group thereto and HCl by-products. A monolayer of oxygen has now been added on top of the previously deposited monolayer of silicon. This second deposition step is also self-limiting; further exposure to H2O results in little additional deposition. These two deposition steps may be repeated to deposit a silicon oxide film having a desired thickness. This prior art deposition method is limited to relatively high substrate temperature and low growth rates.
A catalyst, e.g. pyridine, may be introduced sequentially, following exposure of the surface to the silicon source described above in order to facilitate deposition at lower substrate temperatures. ALD has been performed in this way at substrate temperatures below 200° C. Introducing an additional step, however, further reduces the already low deposition rate. Concurrent exposure to multiple deposition precursors does not significantly address the low growth and sacrifices the atomic layer control desired for most ALD processes. Furthermore, the presence of chlorine and ammonia in the effluents produces undesirable salts which can incorporate into the depositing film in addition to requiring specialized deposition chamber cleaning procedures. Alternative silicon precursors which do not contain chlorine address the production of undesirable salts but do not address the low growth rates.
Thus, there remains a need for new atomic layer deposition processes and materials to form relatively pure dielectric materials at low temperatures but increased growth rates. This and other needs are addressed in the present application.